Because of environmental concerns, oil-based drilling fluids are less favored than aqueous-based drilling fluids. One problem arises when aqueous-based drilling fluids are used to drill through certain types of shale. Certain water-sensitive clayey shales tend to hydrate very easily. When contacted with an aqueous-base drilling fluid, such shales tend to swell or disperse, creating resistance to bit penetration and fouling of the drilling fluid by the dispersed shale.
Aqueous-based drilling fluids that would not hydrate water-sensitive shales would be highly desirable.